Method for analyzing metal microparticles, and inductively coupled plasma mass spectrometry method

ABSTRACT

A method for analyzing a sample containing metal fine particles with an inductively coupled plasma mass spectrometer. The method enables analysis of the sample without the need of standard metal fine particles. Specifically, the present invention relates to a method for analyzing metal fine particles in liquid by use of an inductively coupled plasma mass spectrometer. In the method, the analysis apparatus is provided with a standard solution introduction apparatus including a standard solution storage unit for storing a standard solution containing a specific element in a known concentration, a syringe pump for suctioning and discharging the standard solution, and a solution introduction unit having a standard solution nebulizer and a standard solution spray chamber that are supplied with the standard solution, the standard solution is directly supplied to the standard solution nebulizer at a flow rate of 3 μL/min or less.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of and claims the benefit ofco-pending U.S. application Ser. No. 17/043,406 filed on Sep. 29, 2020as a U.S. national phase entry of International Appln. No.PCT/JP2019/033880 filed on Aug. 29, 2019, all of which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a method for analyzing metal fineparticles contained in liquid or gas, and an inductively coupled plasmamass spectrometry technique using the analysis method.

BACKGROUND ART

In recent years, it has been known that an inductively coupled plasmamass spectrometer (hereinafter, sometimes abbreviated as ICP-MS) is usedfor analysis of metallic impurities in chemical solution or gas used ina semiconductor industry. The metal to be analyzed is sometimes presentas metal fine particles in liquid or gas, and the metal fine particlesare known to be analyzed with ICP-MS.

As shown in FIG. 1 , an apparatus configured to analyze a solutionsystem in the ICP-MS includes a sample storage section 101 for storing asample solution to be measured; a sample introduction section having asample nebulizer 102 and a sample spray chamber 103; a torch section 104for ionizing a sample by forming a plasma; an interface section 105 fortaking ions from the plasma; a mass analysis section 106 for separatingions; and a detection section 107 for detecting the separated ions. Inthe ICP-MS, atoms of a metal element contained in the sample solutionare ionized, and some of the ionized atoms reach a detector by passingthrough the mass analysis section and are detected as pulse counts. Ingeneral, at the time when 10⁴ to 10⁶ atoms are introduced into a plasma,and ionized, one ion reaches a detector, and is detected as a signalintensity of 1 count.

When a concentration of metal dissolved in a sample solution is analyzedin the ICP-MS, a calibration curve (concentration vs signal intensity)obtained by analyzing a standard solution containing the metal is used(for example, Patent Document 1). A calibration curve of signalintensity against metal concentration of a standard solution is preparedbeforehand, and a metal concentration in a sample solution is measuredfrom the signal intensity in the sample solution.

On the other hand, when a sample solution with metal mixed in a solutionas metal fine particles is analyzed, a standard solution containing apredetermined amount of metal fine particles having a known particlediameter is analyzed beforehand to measure the number of metal fineparticles obtained from a detector and a signal intensity per metal fineparticle. In the detector, when one metal fine particle is detected, asignal intensity corresponding to an ion of a metal element forming themetal fine particle appears as a peak, and therefore the number of thepeaks is measured as the number of the metal fine particles reaching thedetector. In addition, the signal intensity correlates with a particlediameter of the metal fine particle.

Specifically, an example will be described in which metal (tentativelycalled metal A) fine particles having a particle diameter of 50 nm areused as a standard. Hereinafter, an imaginary metal element (A) is usedfor the sake of convenience of explanation. When a standard solution isused in which metal (A) fine particles having a particle diameter of 50nm and serving as a standard are present at a concentration of 10⁶particles per mL, the standard solution is suctioned into a nebulizer ata rate of 1 μL/sec, and analyzed. If detector detects 100 metal (A) fineparticles per second, a ratio of metal (A) fine particles passingthrough a spray chamber is 10% because 100 particles are actuallydetected among 1,000 particles introduced into the nebulizer per second.In addition, when the signal intensity from one metal (A) fine particleis 50 counts, a weight of metal (A) fine particles having a 50 nmparticle diameter (654 ag), which is obtained from a volume of metal (A)fine particles having a particle diameter of 50 nm (6.54×10⁻¹⁷ cm³) anda density of metal (A) fine particles having a particle diameter of 50nm (tentatively set to 10 g/cm³), is divided by the signal intensity (50counts) to obtain a weight sensitivity value (654/50=13.08 ag/count) percount. The weight sensitivity value per count from metal (A) fineparticles shows a signal intensity detected with respect to an absoluteamount of metal (A) fine particles introduced into a torch section, andwhen the sample solution to be measured contains metal (A) fineparticles, a particle diameter of metal (A) fine particles in the samplesolution can be calculated from a signal intensity value from one metal(A) fine particle which is obtained as a result of detecting the signalintensity.

In addition, for analyzing the concentration of metal (A) fine particlesin the sample solution, transmission efficiency of a sample spraychamber in a sample introduction section is required to be measuredbeforehand. In this spray chamber, only fine aerosols, among aerosolsformed by the nebulizer with the aid of argon gas, are selected, andintroduced to the torch section. A ratio of an amount of liquid, whichis fed to the torch section from the spray chamber, to an amount ofliquid suctioned into the nebulizer is called transmission efficiency ofthe spray chamber. The transmission efficiency can be calculated fromthe number of particles, which is determined with the metal (A) fineparticles as a standard, but it is very difficult to determine theaccurate number of particles in the standard solution. Thus, a method isused in which transmission efficiency of the spray chamber is determinedfrom a ratio of a sensitivity over a range from the nebulizer to thedetector to a sensitivity over a range from the plasma in the torchsection to the detector. That is, the transmission efficiency isdetermined by comparing a weight sensitivity value per count over arange from the nebulizer to the detector, which is obtained by analyzinga metal (A) standard solution having a known concentration by ICP-MS,with a weight sensitivity value per count over a range from the plasmain the torch section to the detector, which is obtained with a standardsolution containing metal (A) fine particles having a known particlediameter.

Specifically, a standard solution having a metal (A) concentration of 1ppb (1 pg/μL) is suctioned into the nebulizer at a rate of 1 μL/sec toperform analysis. When the detector detects 10,000 counts per second, aweight sensitivity value per count over a range from the nebulizer tothe detector (10⁶/10⁴=100 ag/count) is obtained from an introductionrate into the nebulizer (1 pg/sec=10⁶ ag/sec). The weight sensitivityvalue per count in introduction into the nebulizer represents a signalintensity detected with respect to the weight (absolute amount) of metal(A) introduced into the nebulizer. Thus, the weight sensitivity value ofthe metal (A) fine particles per count over a range from the plasma inthe torch section to the detector is divided by the weight sensitivityvalue per count in introduction into the nebulizer (13.08/100=0.13) todetermine transmission efficiency (13%) through the spray chamber used.That is, it is shown that 13% of the amount of liquid suctioned into thenebulizer is equal to the amount of liquid fed to the torch section fromthe spray chamber used. When the transmission efficiency of the spraychamber is known, the introduction rate into the torch section is known,and therefore the introduction rates of elements other than the elementof metal (A) fine particles having a known particle diameter into thetorch section is determined, so that concentrations of metal fineparticles of those elements in the sample solution can be calculated.

When a sample solution present in liquid in a state of metal fineparticles is analyzed by ICP-MS, it is necessary to prepare a standardsolution containing metal fine particles having a known particlediameter. For elements such as Au, metal fine particles having a knownparticle diameter are commercially available, but for many metalelements that can be analyzed by ICP-MS, it is extremely difficult toprepare metal fine particles having a known particle diameter. Inaddition, when a standard solution is prepared with metal fine particlesof Au having a known particle diameter, accurate control of a particlediameter and the number of particles involves very difficult operationdue to aggregation, dissolution and the like of the fine particles, andthe analysis cannot be quickly performed.

In addition, in inductively coupled plasma mass spectrometry, analysisof a sample gas with a gas containing metal fine particles; and analysiscalled laser ablation ICP-MS in which a solid sample is irradiated withlaser light to evaporate and atomize the sample, and the atomized sampleis directly analyzed (for example, Patent Document 2). In analysis ofmetal fine particles in a gas phase as described above, it is difficultto prepare metal fine particles having a known particle diameter formany metal elements that can be analyzed by ICP-MS, and therefore themetal fine particles in the gas phase cannot be efficiently analyzed.

RELATED ART DOCUMENT Patent Documents

Patent Document 1: JP H3-108246 A

Patent Document 2: JP 2018-136190 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Against the background of the above circumstances, an object of thepresent invention is to provide a method for analyzing metal fineparticles, in which a sample containing metal fine particles to bemeasured is analyzed with an inductively coupled plasma massspectrometer, the method enabling a particle diameter of specificelement metal fine particles to be obtained by using a standard solutioncontaining a specific element without the need of standard metal fineparticles. Another object of the present invention is to provide aninductively coupled plasma mass spectrometry method for measuring thenumber and the concentration of the metal fine particles contained inthe sample by using the method for analyzing metal fine particles.

Means for Solving the Problems

The present inventors have found that when a standard solution having aspecific element in a known concentration is directly supplied to anebulizer at an extremely low flow rate, substantially 100% (totalamount) of the standard solution introduced from a spray chamber to atorch section can be introduced into a plasma. Thus, the presentinventors have arrived at the present invention.

The present invention provides a method for analyzing metal fineparticles in liquid by use of an inductively coupled plasma massspectrometer including: a sample storage section for storing a samplesolution to be measured; a sample introduction section having a samplenebulizer and a sample spray chamber; a torch section for ionizing thesample by forming a plasma; an interface section for taking ions fromthe plasma; a mass analysis section for separating ions; and a detectionsection for detecting the separated ions, in which the inductivelycoupled plasma mass spectrometer is provided with a standard solutionintroduction apparatus including a standard solution storage unit forstoring a standard solution containing a specific element in a knownconcentration, a syringe pump for suctioning and discharging thestandard solution, and a solution introduction unit having a standardsolution nebulizer and a standard solution spray chamber that aresupplied with the standard solution, a standard solution introductionpassage for introducing the standard solution flowing out from thestandard solution spray chamber is connected to a flow passageconnecting the sample introduction section to the torch section, thestandard solution is directly supplied to the standard solutionnebulizer at a flow rate of 3 μL/min or less to introduce the standardsolution into the torch section from the solution introduction unit, anda standard solution sensitivity value that is a specific element weightper count is determined based on a standard solution signal intensityobtained from a detector and a physical amount of the introducedspecific element, and a particle diameter value of metal fine particlesof the specific element is calculated from a sample solution signalcount number of one metal fine particle of the specific element, whichis obtained from the detector by introduction of the sample solution,and the standard solution sensitivity value.

The present invention relates to an inductively coupled plasma massspectrometry method for analyzing a metal fine particle number and ametal fine particle concentration by use of the standard solutionsensitivity value in the method for analyzing metal fine particles inliquid, in which a sample standard solution containing a specificelement in a known concentration is introduced into the torch sectionfrom the sample introduction section, and a sample introduction sectionsensitivity value that is a specific element weight per sample standardsolution signal intensity count is calculated from a sample standardsolution signal intensity obtained from the detector, transmissionefficiency of the sample spray chamber is calculated from the standardsolution sensitivity value and the sample introduction sectionsensitivity value, the number of specific element metal fine particlescontained in the sample solution is calculated from the number ofspecific element metal fine particles obtained from the detector byintroducing a sample solution to be measured into the torch section fromthe sample introduction section for a certain period of time, and thetransmission efficiency of the sample spray chamber, and a total weightof specific element metal fine particles contained in the samplesolution is calculated from a total integrated value of specific elementmetal fine particle signal intensities obtained from the detector byintroduction of the sample solution, the standard solution sensitivityvalue and the transmission efficiency of the spray chamber, and a metalfine particle concentration of the sample solution is calculated from asample solution introduction rate obtained from a flow rate detectionunit provided between the sample storage section and the sampleintroduction section, and the calculated total weight of specificelement metal fine particles.

The present invention also provides a method for analyzing metal fineparticles in gas by use of an inductively coupled plasma massspectrometer including: a gasified sample introduction section forintroducing a sample gas generated by a laser ablation device forevaporating and atomizing a sample by irradiating a solid sample to bemeasured with laser light, or a gas exchange device for replacing byargon gas with a gas component of a sample gas containing an object tobe measured; a torch section for ionizing the sample by forming aplasma; an interface section for taking ions from the plasma; a massanalysis section for separating ions; and a detection section fordetecting the separated ions, in which the inductively coupled plasmamass spectrometer is provided with a standard solution introductionapparatus including a storage unit for storing a standard solutioncontaining a specific element in a known concentration, a syringe pumpfor suctioning and discharging the standard solution, and a solutionintroduction unit having a standard solution nebulizer and a standardsolution spray chamber that are supplied with the standard solution, astandard solution introduction passage for introducing the standardsolution flowing out from the standard solution spray chamber isconnected to a flow passage connecting the gasified sample introductionsection to the torch section, the standard solution is directly suppliedto the standard solution nebulizer at a flow rate of 3 μL/min or less tointroduce the standard solution into the torch section from the solutionintroduction unit, and a standard solution sensitivity value that is aspecific element weight per standard solution signal intensity count isdetermined based on a standard solution signal intensity obtained from adetector and a physical amount of the introduced specific element, and aparticle diameter value of metal fine particles of the specific elementis calculated from a signal intensity count number of one metal fineparticle of the specific element, which is obtained from the detector byintroduction of the sample gas, and the standard solution sensitivityvalue.

Further, the present invention relates to an inductively coupled plasmamass spectrometry method for analyzing a metal fine particle number anda metal fine particle concentration by use of the standard solutionsensitivity value in the method for analyzing metal fine particles ingas, in which analysis is the number of specific element metal fineparticles obtained from the detector by introducing a sample gas to bemeasured into the torch section from the sample introduction section fora certain period of time, and a metal fine particle concentration of thesample gas is calculated from a total integrated value of specificelement metal fine particle signal intensities obtained from thedetector by introduction of the sample gas, the standard solutionsensitivity value obtained by the method of standard addition and theintroduction rate of the sample gas.

In the method for analyzing metal fine particles in the presentinvention, it is important that the standard solution stably supplieddirectly to the standard solution nebulizer at a flow rate of 3 μL/minor less. Thus, as the syringe pump for suctioning and discharging thestandard solution, a syringe pump having high performance is used.Specifically, it is preferable to use a high performance syringe pumpcapable of stably discharging the solution at a flow rate of 0.1 μL/min.

In the present invention, the standard solution is directly supplied tothe standard solution nebulizer at a flow rate of 3 μL/min or less, andsubstantially 100% (total amount) of the supplied standard solution canbe introduced into a plasma. This was confirmed through the followingverifications. Verification 1: the standard solution sensitivity valuethat is a specific element weight per standard solution signal intensitycount did not change even when the standard solution spray chamber washeated to change the temperature. Verification 2: the sensitivity valueobtained with Au metal fine particles having a known particle diameterwas substantially equal to the standard solution sensitivity value.Verification 3: the introduction rate of the standard solution waschanged, and as a result the signal intensity changed in linear mannerwhen the flow rate was not more than 3 μL/min. When the flow rate wasmore than 3 μL/min, the signal intensity tended to decrease, and aphenomenon was observed in which the standard solution started to betrapped in the standard solution spray chamber. Verification 4: standardsolution sensitivity values obtained by using three nebulizers of thesame type as standard solution nebulizers were compared, and the resultshowed that the relative standard deviation was 1% or less.

Advantageous Effects of the Invention

The present invention enables the particle diameter of metal fineparticles contained in a sample to be measured and the number of metalfine particles and the concentration of metal fine particles containedin the sample to be analyzed without the need of standard metal fineparticles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a conventional inductively coupledplasma mass spectrometer.

FIG. 2 is a schematic diagram of an inductively coupled plasma massspectrometer of the present embodiment.

FIG. 3 is a graph showing a relationship between a standard solutionintroduction rate and a signal intensity.

FIG. 4 is a graph showing a relationship between a standard solutionintroduction rate and a signal intensity of an internal standard.

FIG. 5 is a schematic diagram of an inductively coupled plasma massspectrometer for analysis of sample gas in the embodiment.

FIG. 6 is a graph showing a relationship between a standard solutionintroduction rate and a signal intensity of a specific element.

DESCRIPTION OF EMBODIMENTS

In this embodiment, an example will be described in which asolution-based sample is analyzed. FIG. 2 shows a schematic diagram of aconventional inductively coupled plasma mass spectrometer of the presentembodiment. A standard solution introduction apparatus 2 is connected tothe ICP-MS shown in FIG. 2 . In the standard solution introductionapparatus 2 includes a standard solution storage container 201 forstoring a standard solution, a syringe pump 202 for suctioning anddischarging the standard solution, and a standard solution nebulizer 203and a standard solution spray chamber 204 which are supplied with thestandard solution. The standard solution introduction apparatus 2 alsoincludes a waste container 205 for disposal. As the syringe pump 202, asyringe pump capable of controlling a flow rate of 0.1 to 99.0 μL/min.The control flow rate in this syringe pump is determined by performingcalculation from the physical operation amount of a ball screw used in asyringe forming the syringe pump. The apparatus configuration of themain body of ICP-MS (Model 8800 manufactured by Agilent Technologies)other than the standard solution introduction apparatus 2 is basicallythe same as that shown in FIG. 1 , and a flow passage connecting asample storage section 101 to a sample solution nebulizer 102 isprovided with an optical sensor 108 for measuring the introduction rateof a sample solution introduced into the nebulizer, and an air injectionvalve 109.

A standard solution introduction passage 206 for introducing thestandard solution which flows out from the standard solution spraychamber 204 of the standard solution introduction apparatus 2 isconnected to a flow passage 110 connecting a sample solution spraychamber 103 of a sample introduction section to a torch section 104.

In the present invention, as shown in FIG. 2 , a standard solutionintroduction apparatus is separately installed in the ICP-MS main body,and an introduction flow passage for analysis of a sample solution iskept on the ICP-MS main body side. The reason for this is thatoperations such as change of the sample solution during analysis can bequickly performed, and that when a sample solution containing metal fineparticles to be measured is analyzed, it is necessary to introduce thesample solution into the torch section at a certain degree ofintroduction rate.

When the standard solution is directly supplied to the standard solutionnebulizer 203 at a flow rate of 3 μL/min or less with Ar nebulizer gasflow supplied to the nebulizer 203 is at 0.3 L/min, substantially 100%(total amount) of the supplied standard solution can be introduced intoa plasma. The Ar nebulizer gas flow should be as small as possiblebecause the total Ar gas flow to the plasma of ICP-MS is around 1 L/minand another Ar nebulizer gas flow that is supplied to the nebulizer 102needs at least 0.7 L/min to generate fine aerosol of sample solution.When the maximum Ar gas flow supplied to the nebulizer 203 is at 0.3L/min, the maximum standard solution is 3 uL/min in order to have the100% introduction. This was confirmed through four verifications, whichwill be described below.

<Verification 1> The standard solution sensitivity value that is aspecific element weight per standard solution signal intensity count wasexamined while the standard solution spray chamber was heated to changethe temperature. The standard solution sensitivity value that is aspecific element weight per standard solution signal intensity count wasobtained in the following manner.

As the standard solution, a standard solution containing Au in an amountof 10 ppb {(ng/mL) or (pg/μL) as an alternative unit} was used. Thestandard solution was directly introduced into the standard solutionnebulizer at a flow rate of 1 μL/min, and a signal intensity detectedwas examined. In analysis of the standard solution, pure water wassupplied to the sample solution nebulizer at a flow rate of 0.3 mL/minon the ICP-MS main body side. In addition, argon gas (Ar) was suppliedto the standard solution nebulizer and the sample solution nebulizer.

The signal intensity obtained from the detector was 29,159 counts persecond (29,159 counts/sec). In addition, the absolute amount ofintroduction per second of Au suctioned into the standard solutionnebulizer is 10 pg/min=0.167 pg/sec=167,000 ag/sec. Accordingly, astandard solution sensitive value that is a specific element weight perstandard solution signal intensity count was 167,000/29,159=5.72ag/counts. The temperature of the standard solution spray chamber atthis time was 23° C.

With the base temperature of the standard solution spray chamber set to23° C., the standard solution spray chamber was heated to 120° C., and astandard solution sensitivity value that is a specific element weightper standard solution signal intensity count was determined under asimilar condition. The result showed that the standard solutionsensitivity value was 5.71 ag/counts. From this result, substantially100% (total amount) of the standard solution directly supplied to thestandard solution nebulizer was considered as having been introducedinto the plasma because even when the temperature of the standardsolution spray chamber was changed, the standard solution sensitivityvalue did not change when the standard solution was directly supplied tothe standard solution nebulizer at a flow rate of 1 μL/min.

<Verification 2> Au metal fine particles having a particle diameter of60 nm were used to perform analysis. The signal intensity of one of theAu metal fine particles having a particle diameter of 60 nm was 385counts. Since the volume of one of the Au metal fine particles having aparticle diameter of 60 nm is 1.13E-16 cm³, and the density of Au is19.32 g/cm³, the weight of one Au metal fine particle is 2,183.16 ag.This weight is divided by 385 counts to get 5.67 ag/count. That is, thesensitivity value determined from the signal intensity of one of the Aumetal fine particles having a particle diameter of 60 nm is equivalentto 5.67 ag/count.

Under the same conditions as in verification 1, a standard solutioncontaining Au in an amount of 10 ppb was provided, the standard solutionwas directly suctioned into the standard solution nebulizer at a flowrate of 1 μL/min, and a signal intensity detected was examined. As aresult, the signal intensity obtained from the detector was 29,159counts per second (29,159 counts/sec). This result showed that thestandard solution sensitivity value of the standard solution containingAu was 5.72 ag/counts. The sensitivity value obtained from the Au metalfine particles was compared to the standard solution sensitivity value(5.67/5.72=0.992 (99.2%)), and as a result, substantially 100% (totalamount) of the standard solution directly supplied to the standardsolution nebulizer was considered as having been introduced into theplasma.

<Verification 3> The introduction rate of the standard solution waschanged, and a change in signal intensity of the standard solution wasexamined. A standard solution containing a mixture of four metals ofvanadium (V), nickel (Ni), lead (pb) and uranium (U) was introduced intothe standard solution nebulizer at introduction rates of 0, 1, 2.5, 5.0,7.5 and 10 μL/min, and the signal intensity at each of the introductionrates was examined. The results are shown in FIG. 3 . It was found thatas shown in FIG. 3 , the signal intensity increased in a linear mannerwhen the flow rate was 1 to 5 μL/min.

FIG. 4 shows the result of examination of the signal intensity whenmetal elements Mo and W are used as an internal standard, and theintroduction rate of the standard solution is changed. These metalelements were derived from carbonyl compounds of Mo(CO)₆ and W(CO)₆.These compounds sublimate at normal temperature to generate a certaingas vapor. FIG. 5 shows a schematic diagram of an inductively coupledplasma mass spectrometer in analysis of Mo and W as an internalstandard. The inductively coupled plasma mass spectrometer is the sameas in FIG. 2 for the range from torch section 104 to the detectionsection 107 in the ICP-MS main body 1, and the standard solutionintroduction apparatus 2. The inductively coupled plasma massspectrometer is different from that in FIG. 2 in that a gas exchangedevice 301 is provided at the sample solution spray chamber. The gasexchange device 301 replaces by argon gas with a gas component of asample gas containing an object to be measured. In addition, a metalstandard gas generator 302 and a metal standard gas introduction passage303 are connected to the flow passage 110 connecting the gas exchangedevice 301 (the arrow directed to the gas exchange device 301 indicatesintroduction of sample gas) to the torch section 104. The argon gas isintroduced into the metal standard gas generator 302 (the arrow directedto the metal standard gas generator 302 indicates introduction of argongas), and the carbonyl compounds of Mo(CO)₆ and W(CO)₆ are put in themetal standard gas generator 302.

Mo and W sublimated with the argon gas at a constant flow rate of 0.2L/min were introduced into the torch section 104 through the metalstandard gas introduction passage 303 while the standard solution wasintroduced with the apparatus shown in FIG. 5 . The introduction ratesof the standard solution were 0, 1, 2.5, 5.0, 7.5 and 10 μL/min, and thesignal intensity of Mo and W at each of the introduction rates wasexamined. At this time, the argon gas flew out from the gas exchangedevice 301 (flow rate: 0.8 mL/min).

It was confirmed that as shown in FIG. 4 , the signal intensity of Moand W as an internal standard tended to decrease as the introductionrate of the standard solution increased. The signal intensity of theinternal standard corresponds to the sensitivity of the ICP-MS mainbody, and as long as the sensitivity of the ICP-MS main body does notchange, the signal intensity is constant when Mo and W as an internalstandard are introduced at a constant flow rate. However, as shown inFIG. 4 , the signal intensity of Mo and W as an internal standard tendsto decrease as the introduction rate of the standard solution increases,which shows that the sensitivity of the ICP-MS main body tends todecrease as the introduction rate of the standard solution increases.Thus, it was found that when a sample gas was analyzed by use of a laserablation device or a gas exchange device, it was possible to maintainICP-MS at a high sensitivity by performing control so that theintroduction rate of the standard solution was as low as possible.

A standard solution containing a mixture of three metals of iron (Fe),copper (Cu) and zinc (Zn) was introduced into the standard solutionnebulizer at an introduction rate of 3.0 μL/min or less, and the signalintensity at the introduction rate was examined. The results are shownin FIG. 6 . FIG. 6 shows results for three metals in parallel, and ineach graph, the ordinate represents a signal intensity (count), and theabscissa represents an introduction rate. It was found that for thethree metals, the signal intensity increased in a linear manner when theflow rate was 3.0 μL/min or less. From this result, substantially 100%(total amount) of the standard solution directly supplied to thestandard solution nebulizer was considered as having been introducedinto the plasma when the standard solution was directly supplied to thestandard solution nebulizer at a flow rate of 3 μL/min or less. When theflow rate was more than 3 μL/min, the signal intensity tended todecrease, and a phenomenon was observed in which the standard solutionstarted to be trapped in the standard solution spray chamber.

<Verification 4> Standard solution sensitivities obtained via threenebulizers of the same type as standard solution nebulizers werecompared. As the standard solution, a standard solution containing amixture of three of vanadium (V), lead (Pb) and uranium (U) was used. Asconditions, a standard solution of a mixture of the three metals with aconcentration of 10 ng/mL was introduced from the standard solutionnebulizer at a flow rate of 1 μL/min. The other conditions are the sameas in the case of the standard solution in verification 3.

In addition, the signal intensity was examined with three metals of Cr,Mo and W used as internal standard metal elements. The three metals asan internal standard were derived from carbonyl compounds, andintroduced by the method described in FIG. 5 for verification 3. Cr, Moand W sublimated with the argon gas at a flow rate of 0.2 L/min wereintroduced into the torch section 104 through the metal standard gasintroduction passage 303 while the standard solution was introduced. Atthis time, the argon gas flew out from the gas exchange device 301 (flowrate: 0.8 mL/min). The optimum total Ar gas flow for gas analysisbecomes around 1.3 L/min that is higher than the analysis of normalaqueous analysis.

Table 1 shows the results of examination of the signal intensities ofthe metal elements when three nebulizers of the same type are used asstandard solution nebulizers.

TABLE 1 Standard solution Internal standard V Pb U Cr Mo W Nebulizer-135,278 378,438 798,065 111,615 45,460 88,481 Nebulizer-2 36,077 391,145829,978 111,389 44,435 88,354 Nebulizer-3 35,732 393,829 833,304 110,55344,054 86,670 SD   401  8,221  19,456    559   727  1,011 Average 35,695387,804 820,449 111,186 44,650 87,835 RSD (%)    1.12     2.12     2.37    0.50    1.63    1.15

For each of the relative standard deviations in the signal intensitiesof the elements shown in Table 1, subtraction of the relative standarddeviation of the internal standard from the relative standard deviationof the standard solution in consideration of stability of the ICP-MSmain body gave a relative standard deviation value of less than about1%. The relative standard deviation of less than about 1% showsstability when three nebulizers of the same type are changed from one toanother. In typical analysis with ICP-MS, the common introduction rateof a solution into a nebulizer is 200 μL/min, and at this level ofsolution introduction rate, changing of the nebulizer even to anebulizer of the same type causes a significant change in signalintensity, so that the relative standard deviation is about 20%.However, introduction of the standard solution into the standardsolution nebulizer at a flow rate of 1 μL/min was found to cause littlechange in signal intensity even when the nebulizer was changed to threenebulizers of the same type. Thus, substantially 100% (total amount) ofthe standard solution directly supplied to the standard solutionnebulizer was considered as having been introduced into the plasma whenthe standard solution was directly supplied to the standard solutionnebulizer at a flow rate of 1 μL/min or less.

From the results of the above four verifications, it was determined thatwhen the standard solution is directly supplied to the standard solutionnebulizer at a flow rate of 3 μL/min or less with 0.3 L/min of Arnebulizer gas, substantially 100% (total amount) of the suppliedstandard solution can be introduced into a plasma.

A method for measuring the particle diameter of metal fine particles,and a method for measuring the number of metal fine particle and theconcentration of metal fine particles in a sample solution will now bedescribed. As shown in verification 1, when a standard solutioncontaining Au in an amount of 10 ppb is used, a signal intensitydetected when a standard solution is directly suctioned into thestandard solution nebulizer at a flow rate of 1 μL/min shows that astandard solution sensitive value that is a specific element weight perstandard solution signal intensity count is 167,000/29,159=5.72ag/counts.

Next, a sample solution containing Au metal fine particles having anunknown particle diameter was put in the sample storage section, thesample solution was suctioned into the sample solution nebulizer at aflow rate of 60 μL/min (1 μl/sec) for 1 minute, and a signal intensitydetected was examined. In analysis of the sample solution, pure waterwas supplied to the standard solution nebulizer at a flow rate of 1μL/min in the standard solution introduction apparatus. In addition,argon gas (Ar) was supplied to the standard solution nebulizer and thesample solution nebulizer.

The detection result obtained with the sample solution showed that thesignal intensity per Au metal fine particle in the sample solution was381 counts. In this case, the total weight of one Au metal fine particledetected is 5.72×381=2,183.9 ag. From the total weight and the densityof Au (19.32 g/cm³), a volume was calculated, and from the volume, aparticle diameter was calculated. The result showed that the metal fineparticle had a particle diameter of 60 nm (the volume was calculated as2,183.9/19.32=1.13E−16 cm³, and the particle diameter was calculatedfrom the equation: sphere volume=4πr³/3. The physical amount of aspecific element in the present invention includes the atomic weight ofthe specific element and the density of the specific element.

In the detector, when one Au metal fine particle is detected, a signalintensity corresponding to an ion of a metal element forming the metalfine particle appears as a peak, and therefore the number of the peaksis measured as the number of the Au metal fine particles reaching thedetector. The number of Au metal fine particles reaching the detectorper minute was 1300. In addition, the average signal intensity of thepeaks was 30 counts.

Measurement of transmission efficiency of the sample solution spraychamber will now be described. A sample standard solution containing Auin an amount of 1 ppb was provided as a sample solution, the samplestandard solution was suctioned into the sample solution nebulizer at aflow rate of 60 μL/min, and a signal intensity detected was examined. Inanalysis of the standard solution, pure water was supplied to thestandard solution nebulizer at a flow rate of 1 μL/min on the ICP-MSmain body side. In addition, argon gas (Ar) was supplied to the standardsolution nebulizer and the sample solution nebulizer. The flow rate ofthe sample standard solution is measured by feeding an air bubble intothe solution from an air injection valve, sensing the air bubble withtwo optical sensors, and calculating a movement speed between twopoints.

A signal intensity of 20,000 counts was detected per second with thesample standard solution. The introduction rate into the sample solutionnebulizer is 1 pg/sec=1,000 fg/sec=1,000,000 ag/sec.

The sample introduction section sensitivity value that is a specificelement weight per sample standard solution signal intensity count is 50ag/count. As shown in verification 1, the standard solution sensitivityvalue is divided by the sample introduction section sensitivity value(5.72/50=0.114) to obtain transmission efficiency of the sample solutionspray chamber (11.4%).

The number of Au metal fine particles in the sample solution can becalculated with the transmission efficiency of the sample solution spraychamber into consideration. As described above, it is shown that 60 μLof the sample solution contained 11,403 (1,300/0.114) Au metal fineparticles because 1300 Au metal fine particles were detected per minutein analysis of the sample solution containing Au metal fine particles.

The average signal intensity of 1,300 particles, which is obtained withthe sample solution, is 30 counts, the total integrated value of Aumetal fine particle signal intensities per minute is 1,300×30=39,000counts, and the total weight of Au is 5.72×39,000=223,080 ag. When thetransmission efficiency of the spray chamber is taken intoconsideration, the total weight of Au in the sample solution is223,080/0.114=1,956,842 ag. Since the volume of 60 μL includes the totalweight of Au, the Au metal fine particle concentration of the samplesolution is 1,956,842/60=32,614 ag/μL=32.6 fg/μL=0.032 pg/μL (ppb).

Analysis of a solution-based sample has been described above. When metalfine particles contained in gas are analyzed, a laser ablation devicefor irradiating a solid sample to be measured with laser light toevaporate and atomize the sample, or a gas exchange device for replacingby argon gas a gas component of a sample gas containing an object to bemeasured is used. In analysis of metal fine particles contained in gasas described above, a sample gas generated by the laser ablation deviceor the gas exchange device is directly introduced into the torchsection. In analysis of such a sample gas, a nebulizer or a spraychamber as used for the solution-based sample is not used, substantially100% (total amount) of the sample gas supplied to the torch section isintroduced into a plasma. Analysis of the sample gas corresponds to theapparatus schematic diagram shown in FIG. 5 . In FIG. 5 , a gas exchangedevice is provided, and by providing a laser ablation device at theplace of the gas exchange device, a fixed sample can be analyzed. Theparticle diameter of metal fine particles contained in the sample gascan be calculated only by analyzing the standard solution with theapparatus shown in FIG. 5 .

The number of metal fine particles of the specific element in the samplegas is accumulated through measuring the number of peaks of theparticles from the detection result with the sample gas. Theconcentration of metal fine particles of the specific element in thesample gas can be calculated from the total integrated value of specificelement metal fine particle signal intensities obtained from thedetector by introduction of the sample gas, and the introduction rate ofthe sample gas.

INDUSTRIAL APPLICABILITY

In the present invention, the particle diameter of metal fine particlescontained in a sample can be measured and the number of metal fineparticles and the concentration of metal fine particles contained in thesample can be analyzed without the need of standard metal fineparticles. Thus, various analyses such as continuous real-timemonitoring of metal fine particles in the air, analysis of mercury (Hg)in the air and exhaust gas, analysis of metal components in cigarettesmoke, and analysis of a very small amount of metal impurities invarious kinds of gases that are used in production of semiconductors canbe quickly and efficiently performed with ICP-MS.

REFERENCE SIGNS LIST

-   -   1 ICP-MS (main body)    -   101 Sample storage section    -   102 Sample solution nebulizer    -   103 Sample solution spray chamber    -   104 Torch section    -   105 Interface section    -   106 Mass analysis section    -   107 Detector    -   108 Optical sensor    -   109 Inflation valve    -   110 Flow passage    -   2 Standard solution introduction apparatus    -   201 Standard solution storage container    -   202 Syringe pump    -   203 Standard solution nebulizer    -   204 Standard solution spray chamber    -   205 Waste container    -   206 Standard solution introduction passage    -   301 Gas exchange device    -   302 Metal standard gas generator    -   303 Metal standard gas introduction passage

1. A method for analyzing metal fine particles in gas by use of aninductively coupled plasma mass spectrometer, the spectrometercomprising: a gasified sample introduction section for introducing asample gas generated by a laser ablation device for evaporating andatomizing a sample by irradiating a solid sample to be measured withlaser light, or a gas exchange device for replacing by argon gas with agas component of a sample gas containing an object to be measured; and atorch section for ionizing the sample by forming a plasma; an interfacesection for taking ions from the plasma; a mass analysis section forseparating ions; and a detection section for detecting the separatedions, wherein the method comprises the steps of: providing theinductively coupled plasma mass spectrometer with a standard solutionintroduction apparatus comprising a storage unit for storing a standardsolution containing a specific element in a known concentration, asyringe pump for suctioning and discharging the standard solution, and asolution introduction unit having a standard solution nebulizer that issupplied with the standard solution, and a standard solution spraychamber combined with the standard solution nebulizer, connecting astandard solution introduction passage for introducing the standardsolution flowing out from the standard solution spray chamber to a flowpassage connecting the gasified sample introduction section to the torchsection, supplying the standard solution directly to the standardsolution nebulizer at a flow rate of 3 μL/min or less to introduce thestandard solution into the torch section from the solution introductionunit, and determining a standard solution sensitivity value that is aspecific element weight per standard solution signal intensity countbased on a standard solution signal intensity obtained from a detectorand a physical amount of the introduced specific element, andcalculating a particle diameter value of metal fine particles of thespecific element from a signal intensity count number of one metal fineparticle of the specific element, which is obtained from the detector byintroduction of the sample gas, and the standard solution sensitivityvalue.
 2. An inductively coupled plasma mass spectrometry method foranalyzing a metal fine particle number and a metal fine particleconcentration defined in claim 1 by use of the standard solutionsensitivity value in the method for analyzing metal fine particles ingas, wherein the method comprises the steps of: introducing a sample gasto be measured into the torch section from the sample introductionsection to measure the number of specific element metal fine particlesobtained from the detector, and calculating a metal fine particleconcentration of the sample gas from a total integrated value ofspecific element metal fine particle signal intensities obtained fromthe detector by introduction of the sample gas, the standard solutionsensitivity value and the introduction rate of the sample gas.